Nonhalogenated flame retardant adhesives and tapes

ABSTRACT

Flame retardant adhesives and tape articles include a nonhalogenated flame retardant composition comprising a combination of melamine phosphate and melamine cyanurate.

FIELD

This disclosure relates to adhesives and adhesive articles that includea nonhalogenated flame retardant composition.

BACKGROUND

Flame retardant adhesives and tapes are used in many industries and formany different purposes. They are used, for example, in the electricalindustry as insulating tapes. Flame retardant compositions, widely usedas flame retardant adhesives and tapes, utilize one or morehalogen-containing materials. However, environmental and safety concernsregarding use of halogen-containing materials in adhesives and relatedarticles have been raised and in response to these concerns, manynonhalogenated flame retardant materials have been introduced to be usedin place of halogen-containing materials. In some instances, when largeramounts of nonhalogenated flame retardant materials are used, there canbe undesirable effects, such as reduction in tackiness of the adhesive.U.S. Pat. No. 6,022,914 (Nowack et al.) overcomes this problem byovercoating such an adhesive composition with a thin layer of anadhesive not containing any of the nonhalogenated flame retardantcomposition or a low level of nonhalogenated flame retardant compositionwhich does not inhibit the tackiness of the adhesive.

SUMMARY

Thus, it is desirable to have nonhalogenated, flame retardantcompositions that offer flame resistant properties and also thatmaintain functional adhesive performance. There is also a desire forarticles that contain such compositions.

With the present invention, it was unexpectedly found that althoughmelamine phosphate and melamine cyanurate flame retardants individuallyachieved only a CTI rating of IIIa, when the two were combined, theyachieved a CTI rating of I.

In one aspect, flame retardant adhesives are provided that are useful,for example, in the construction of tapes. The flame retardant adhesivesinclude a flame retardant composition that includes a melamine phosphateand a melamine cyanurate.

In another aspect, a tape construction is provided that includes asupport material that is substantially free of halogenated materials,has at least two major surfaces, an adhesive disposed on at least onemajor surface of the support material and a flame retardant compositionthat includes a melamine phosphate and a melamine cyanurate. The flameretardant composition can be present in or incorporated into either orboth of the adhesive and the support material. The flame retardantcomposition may also be present as or incorporated into an independentstructural or functional layer within the tape construction.

Thus, adhesives and tapes are provided that offer desired flameretardant properties, are simple to make and use, and provide acceptableperformance as an adhesive or a tape.

The above summary is not intended to describe each disclosed embodimentof every implementation of the present disclosure. The detaileddescription which follows more particularly exemplifies illustrativeembodiments.

DETAILED DESCRIPTION

It is to be understood that other embodiments are contemplated and maybe made without departing from the scope or spirit of the presentdisclosure. The following detailed description, therefore, is not to betaken in a limiting sense.

Unless otherwise indicated, all numbers expressing feature sizes,amounts, and physical properties used in the specification and claimsare to be understood as being modified in all instances by the term“about.” Accordingly, unless indicated to the contrary, the numericalparameters set forth in the foregoing specification and attached claimsare approximations that can vary depending upon the desired propertiessought to be obtained by those skilled in the art utilizing theteachings disclosed herein. The use of numerical ranges by endpointsincludes all numbers within that range (e.g., 1 to 5 includes 1, 1.5, 2,2.75, 3, 3.80, 4, and 5) and any range within that range.

In this disclosure,

“halogen-free” and “nonhalogenated” are used inter-changeably herein andrefer to the substantial absence, e.g., trace or ineffective amounts, ofhalogens, i.e., fluorine, chlorine, bromine, iodine, and astatine;

“flame retardant compositions” refers to halogen-free or nonhalogenatedflame retardant or flame resistant compositions;

“flame retardant materials” refer to one or more nonhalogenated flameretardant materials that make up the flame retardant compositionspresented herein;

“flame retardant adhesives or tapes” refer to adhesives and tapesincorporating flame retardant compositions presented herein that canpass the requirements set forth by the flame test of industry standardUL 510 (Underwriters Laboratories Inc., Eighth Edition);

“melamine phosphate(s)” refers to melamine monophosphate(s), melaminepolyphosphate(s), and melamine pyrophosphate(s); and

“halogen-free flame retardant” and “nonhalogenated flame retardant”refer to flame retardant compositions that do not contain halogens.

Acceptable adhesive performance refers to meeting the requirements asset forth by the adhesion test included in ASTM D1000-04 (Standard TestMethods for Pressure-Sensitive Adhesive-Coated Tapes Used for Electricaland Electronic Applications). Acceptable insulation performance refersto meeting the requirements as set forth by UL 510 in regards todielectric strength, before and after humidity exposure, and insulationresistance. Said tests are based on ASTM D-149-97a (Standard Test Methodfor Dielectric Breakdown Voltage and Dielectric Strength of SolidElectrical Insulating Materials at Commercial Power Frequencies, 2004),which provides standard procedures for the determination of dielectricstrength of solid insulating materials at commercial power frequencies,under specified conditions. In addition, insulation performance refersto the evaluation of the Comparative Tracking Index (“CTI”) or the ASTMD-149-97a test. The CTI test is used to measure material degradationproperties under electrical stress (tracking) of an insulating materialas set forth in ASTM D3638-07 (Standard Test Method for ComparativeTracking Index of Electrical Insulating Materials, 2007).

Adhesives and tape constructions are provided that are flame retardant.An adhesive or a tape can be considered flame retardant when it caninhibit or resist spread of fire. According to the flame test describedin UL510 standard, in order for an adhesive or a tape test specimen tobe considered flame retardant, when a test flame is applied to the testspecimen, it can not flame longer than 60 seconds following any of five15 seconds applications of the test flame, the period betweenapplications being: a) 15 seconds if the specimen flaming ceases within15 seconds; or b) the duration of the specimen flaming if the specimenflaming persists longer than 15 seconds. The test specimen should notignite combustible materials in its vicinity or damage more than 25percent of the indicator flag during, between, or after the fiveapplications of the test flame.

The flame retardancy of the disclosed adhesives and tapes is provided bythe included flame retardant compositions. The disclosed flame retardantcompositions are nonhalogenated and include a combination of twoparticular flame retardant materials: melamine phosphate and melaminecyanurate. Optionally, the flame retardant compositions may also includeone or more additional nonhalogenated flame retardant materials such asalumina trihydrate (Al₂O₃.3H₂O) and magnesium hydroxide (Mg(OH)₂).Commercially available examples of include, but are not limited to thoseavailable under the trade designations HYMOD (Huber Corp., Edison, N.J.)or POLYFILL (R. E. Carroll, Inc., Trenton, N.J.). However, thesematerials should not be added in amounts that would lower the CTI ratingof the flame retardant composition. These compositions may be part ofthe adhesive or incorporated into the tape construction or disposed onthe backing as a separate layer or a combination thereof.

The melamine phosphate portion of the flame retardant composition isrepresented by:

Wherein

when n=1 it's melamine (mono)phosphate,

when n=2 it's melamine pyrophosphate, and

when n=3 it's melamine polyphosphate

Commercially available examples of suitable melamine phosphates include,but are not limited to those available under the trade designationsMPP-B, a melamine pyrophosphate, available from Kuo Fong Enterprises,Taiwan, MELAPUR 200, a melamine polyphosphate, available from Ciba (nowpart of BASF), Germany; and BUDIT 3141, a melamine polyphosphate,available from Budenheim, Spain.

The melamine cyanurate portion of nonhalogenated flame retardantcomposition is represented by:

Commercially available examples of suitable melamine cyanurates include,but are not limited to those available under the trade designationsMELAPUR MC 15, available from Ciba (now part of BASF), Germany; CG-610,available from Chemgarde, Taiwan.

The weight ratio of melamine phosphate to melamine cyanurate may be fromabout 1:6 to about 2:1.

The total amount of flame retardant compositions as well as the amountsof each of the flame retardant materials that make up the total amountof flame retardant composition used may be varied over a wide range butare present in an amount sufficient to render the adhesive or tape flameretardant. As the total amount of flame retardant and/or the relativeamounts of flame retardant materials that make up the flame retardantare changed, the performance properties such as adhesion may beadversely affected depending on the intended application for theadhesive or tape. Within these parameters, a preferred lower limit forthe flame retardant in the flame retardant adhesive or backing can beabout 30% by weight (30 wt %), and in some cases about 35 wt % and yetin other cases about 38 wt %. A preferred upper limit can be about 60 wt%, and in some cases about 50% wt % and yet in other cases about 40 wt%.

In some embodiments, the disclosed flame retardant composition offersdesired flame retardant properties without substantially affectingfunctional performance of the adhesives and tapes, such as failure ofadhesion to an intended surface or reduction in insulating properties ofan insulating tape. Exemplary adhesive and tape constructions with flameretardant compositions containing appropriate amounts of the combinationof melamine phosphate and melamine cyanurate, together with or withoutone or more additional flame retardant materials incorporated, showadvantageous properties and characteristics in comparison to theirproperties individually. Specifically, as shown in Table 2, when eitherof the melamine phosphate or melamine cyanurate flame retardantmaterials of the composition are present individually in adhesives ortape constructions they only achieve a CTI rating of IIIa. Surprisingly,synergistic results are obtained when the provided flame retardantcompositions are used at appropriate levels in the adhesives or tapeconstructions whereby CTI ratings of I are achieved. For example, asshown in Table 3, adhesives and tape constructions with the appropriateflame retardant combination of the present invention can pass theindustry standard UL 510 flame retardancy test and can achieve aComparative Tracking Index (“CTI”) rating of I.

In various embodiments of the invention, the flame retardantcompositions can be included within an adhesive material in order toimpart desired flame retardant properties to the adhesives. Usefuladhesives include many different types and forms, such as pressuresensitive adhesives, thermoset adhesives, hot-melt adhesives, and othertypes of adhesives. As is well known in the art, when described by theirrelative chemical compositions, adhesives may be grouped as acrylicadhesives, polyolefin adhesives, styrenic co-polymer adhesives, siliconeadhesives, epoxy adhesives, ethylene co-polymer adhesives, and othertypes of adhesives. The provided nonhalogenated flame retardantcompositions may be incorporated into any of these adhesive materials toimpart desired flame retardant properties to the adhesives.

The provided flame retardant compositions may also be used in adhesivesor tape constructions together with other materials. Many adhesives, forexample, include one or more cross-linking compositions such as, forexample, a bis-amide. Adhesives or tape constructions also oftenincorporate one or more tackifier compounds to manage a desired tackcharacteristic of the adhesive or tape. Inclusion of other customaryadditives, adjuvants, agents and materials (e.g., colorants, pigments,primers, fillers, UV absorbers, and conductive particles) are understoodby those skilled in the art.

Adhesives incorporating the provided flame retardant compositions may beused in any application for which the underlying adhesive without theflame retardant composition is intended and for which a degree of flameretardancy is desired. The provided flame retardant compositions alsofind particular utility in tape constructions. Such tape constructionsgenerally comprise a support material onto which one or more functionalor structural layers are applied (typically by coating). One or more ofthe provided flame retardant compositions may be used in or with suchtape constructions by incorporating the flame retardant compositionsinto the support material and/or one or more of the functional orstructural layers. The flame retardant compositions may, for example, beincorporated into an adhesive which is applied to a support material, orit may be applied as, or together with, a non-adhesive layer within thetape constructions independent of an adhesive layer. There is,therefore, great flexibility in the utility of the provided flameretardant compositions within a tape construction.

In at least one embodiment of the disclosure, a multi-layered tapeconstruction includes a flame retardant adhesive applied to a supportmaterial having at least two major surfaces. The flame retardantadhesive is provided as a layer applied to one of the major surfaces ofsupport material. The flame retardant adhesive layer can be of anydesired and workable thickness, but is generally in the range from about12 μm to about 80 μm or even possibly more. The support material is,typically, free of halogen-containing compounds. Suitable supportmaterials include, for example: polymer materials such as polyesters(e.g., PET (polyethylene terephthalate)), polyolefins, polyamides andpolyimides; natural and synthetic rubber materials; paper materials;metal foils, glass cloths; and other types of materials. The supportmaterial can be of any desired and workable thickness, but is generallybetween about 25 μm and about 125 μm thick.

Tape constructions that include the flame retardant compositions of thepresent invention can include primer disposed between flame retardantadhesive and support material. A suitable primer is equivalent to 3M'sP-93 primer (a solvent-based composition with acrylonitrile-butadienepolymer, fatty acids, and alcohol). Flame retardant tape constructionsmay also include a low adhesion backing (or “LAB”) material on the majorsurface of the support material opposite the major surface including theadhesive and, if present, the primer. The low adhesion backing materialcan help prevent individual pieces of tape from adhering to each otherwhen a roll is manufactured and wound. Suitable LAB materials includethose equivalent to 3M's RD-1547 Urethane Polymer Solution.

EXAMPLES

The following examples and comparatives are offered to aid in theunderstanding of the present disclosure and are not to be construed aslimiting the scope thereof. Unless otherwise indicated, all parts andpercentages are by weight. The following test methods and protocols wereemployed in the evaluation of the illustrative and comparative examplesthat follow:

Test Methods

1. UL 510 (section 6) Flame Retardancy Test

A specimen is exposed to an open flame for a period of fifteen seconds.Upon exposure to the flame, any flame on the test specimen (whichtypically catches fire) must extinguish in less than 60 seconds to passthe test. The test is repeated five times. Any extinguishing time longerthan 60 seconds is considered a failure for the specimen.

Results are reported as “Pass” or “Fail.” Further information regardingthe test may be found in the description of the UL 510 standard, EighthEdition, published by Underwriters Laboratory of Northbrook, Ill., USA.

2. UL 510 Ratio of Wet to Dry Dielectric Strength

Testing for dry and wet dielectric strength was performed according tothe protocol of ASTM D149-97a. In general, according to this test asample is placed between two electrodes and power is increased untilthere is a dielectric failure. Testing for “dry” dielectric strength wasperformed at room temperature and 50% relative humidity. Testing for“wet” dielectric strength was performed upon exposure of the sample for96 hours at 23° C. and 96% relative humidity. To pass the dry dielectricstrength test, the dielectrics must be greater than or equal to 1000V/mil. To pass the wet dielectric strength test, at least 90% of the drydielectric strength must be retained (i.e., the wet dielectrics aregreater than or equal to 900 V/mil). To pass UL510, the ratio of wetdielectric breakdown/dry dielectric breakdown must be greater than 90%.

3. UL-510 Adhesive Strength to Steel at Room Temperature (“ATS”)

The Adhesive Strength to Steel at Room Temperature of a tape is ameasure of the force necessary to remove the tape from a prescribedsurface when measured in accordance with ASTM D1000-04. In general,according to this test a sample is placed in crosshead type testingmachine, with two clamps to hold the sample in the same plane and theclamps separate from each other recording the force to remove theadhesive tape from the piece of steel. The minimum passing value is0.454 Kg/in.

4. Comparative Tracking Index (“CTI”) Rating

The Comparative Tracking Index (or “CTI”) Rating of a material is ameasure of the resistance of a material to surface tracking underdefined test conditions. The protocol for the test is set forth in ASTMD3638-07. In general, to perform the test the upper surface of a testspecimen is supported in an approximately horizontal plane and subjectedto an electrical stress via two electrodes. The surface between theelectrodes is subjected to a succession of drops of an electrolytesolution until the over-current device operates, until a persistentflame occurs or until the testing period has elapsed. Individual testsare of short duration (less than 1 hour) with up to 50 or 100 drops ofabout 20 mg of electrolyte solution falling at 30 second intervalsbetween platinum electrodes spaced 40 mm apart on the test specimensurface. An alternating current voltage between 100 Volts and 600 Voltsis applied to the electrodes during the test.

Results are plotted to record the number of drops of electrolytesolution placed on the surface of the specimen versus the recordedvoltage. The Comparative Track Index, or CTI, represents the voltagecorresponding to 50 drops of electrolyte solution. The lower the CTIrating for a given material, the greater is the creepage distanceassociated with that material. A CTI Rating is given as follows:

CTI Rating I: CTI≧600 V

CTI Rating II: 400 V≦CTI<600 V

CTI Rating Ma: 175 V≦CTI<400 V

CTI Rating IIIb: 100 V≦CTI<175 V

Materials Used

Ingredient Product Name Source Acrylic Adhesive 3M Product Number 3MCompany, Polymer (acrylate 21-3314-0004-0 St Paul, MM and acrylic acid(not commercially copolymer) available) Melamine Cyanurate MELAPUR MC 15Ciba (now part of BASF), Germany Melamine Cyanurate CG-610 Chemguard,Taiwan Melamine MPP-B Kuo Fong Enterprise, Pyrophosphate Taiwan MelamineMELAPUR 200 Ciba(now part of BASF), Polyphosphate Germany Melamine BUDIT3141 Budenheim, Spain Polyphosphate Ammonium FR CROS S 10 Budenheim,Spain polyphosphate Pyrophosphoric ZURAN 484 Chitec, Taiwan acid saltsRosin Ester SYLVALITE RE80HP Arizona Chemical, Tackifier Jacksonville,FL Binder (silicone LORIAS ASE-50 Long River Chemical, modified acrylicTaiwan copolymer) TiO2 Titanium Dioxide Dupont, Taipei, Taiwan UrethaneSolution RD-1547 3M Company, St Paul, Polymer (not commercially MNavailable) Primer (solvent- P-93 3M Company, St Paul, based composition(not commercially MN with acrylonitrile- available) butadiene polymer,fatty acids, and alcohol) PET Film TAIRILIN BP25 NanYa, Taoyuan, Taiwan

Comparative Examples C-1 to C-7 and Examples 1-8

To prepare tape samples for each example and comparative example, anadhesive composition was prepared containing the ingredients, andamounts thereof, identified in Tables 1 and 2, below, based on 100 partsof acrylic adhesive polymer, 3M Company product number 21-3314-0004-0.For each sample, the ingredients for the adhesive composition were mixedusing a laboratory-size high intensity mixer in the presence of asolvent (heptane, ethyl acetate or a blend of both). The resultingcomposition was coated directly onto a 26 um thick TAIRILIN BP25 PETfilm, primed with 3M P-93 Primer, using either a laboratory knife-coaterto produce a handspread samples, or a pilot-size coater (equipped with aknife-coater), to produce a continuous coated film with a nominalcoating thickness of about 25 um. After coating, the samples were eitherplaced in a forced-convection oven (in the case of handspread samples)or continuously passed through a tunnel oven (in the case of thecontinuous film) to extract the solvent and dry the sample. The coatedand dried samples were then cut or slit to produce 0.75 inch (1.9 cm)samples. The samples were subjected to the test methodologies describedabove and the results are indicated in Table 2 and Table 3, below.

TABLE 1 Comparative Examples C-1 to C-7 Binder: FR agent: MC FR MC FR MPFR UL 510 Tackifier: LORIAS FR FR agent: agent: agent: agent: UL 510wet/dry UL 510 RE80HP ASE-50 CROSS 10 ZURAN MELAPUR CG-610 MPP-B FRdiel. strength ATS CTI Ex. (phr) (phr) (phr) 484 200 (phr) (phr) (phr)TiO2 (60 sec) .>90% (kg/in) rating C-1 4.4 0 43.4 0 0 0 0 0 Pass Failed.208 302VIIIa C-2 4.5 0 0 43.2 0 0 0 0 Pass Failed .333 351VIIIa C-3 0 00 0 0 80 0 0 Fail Not .548 Not Measured Measured C-4 0 0.3 0 0 0 0 60 12Pass Pass 1.076 300VIIIa C-5 0 0.3 0 0 60 0 0 12 Pass Pass .660 275VIIIaC-6 0 0 0 0 0 10 57 8 Pass Pass .943 300VIIIa C-7 0 0 0 0 0 10 57 0 PassPass .988 275VIIIa

TABLE 2 Examples 1-8 Binder: MC FR MC FR MP FR MP FR UL 510 LORIASagent: agent: agent: agent: wet/dry UL 510 ASE-50 CG-610 MELAPUR MPP-BBUDIT UL 510 FR diel. strength ATS CTI Ex. (phr) (phr) MC 15 (phr) (phr)3141 (phr) TiO2 (60 sec) >90% (kg/in) rating 1 1.4 20 0 40 0 8 Pass Pass.940 600VI 2 1.2 0 33 33 0 0 Pass Pass .944 650VI 3 0.3 29.3 0 29.3 0 0Pass Pass .940 650VI 4 0.3 30.5 0 30.5 0 0 Pass Pass 1.075 675VI 5 0.545 0 0 22 0 Pass Pass .860 650VI 6 0.5 45 0 0 22 8 Pass Pass .875 625VI7 0 57 0 10 0 8 Pass Pass .988 625VI 8 0 57 0 10 0 0 Pass Pass .976625V1

Although the aforementioned detailed description contains many specificdetails for purposes of illustration, one of ordinary skill in the artwill appreciate that many variations, changes, substitutions, andalterations to the details are within the scope of the disclosure asclaimed. Accordingly, the disclosure described in the detaileddescription is set forth without imposing any limitations on the claimeddisclosure. The proper scope of the disclosure should be determined bythe following claims and their appropriate legal equivalents. All of thereferences cited are herein incorporated by reference in their entirety.

1. A flame retardant adhesive comprising: at least one adhesive; and aflame retardant composition, wherein the flame retardant compositioncomprises both a melamine phosphate and a melamine cyanurate.
 2. A flameretardant adhesive according to claim 1, wherein the melamine phosphateis a melamine polyphosphate.
 3. A flame retardant adhesive according toclaim 1, wherein the melamine phosphate is a melamine pyrophosphate. 4.A flame retardant adhesive according to claim 1, wherein the weightratio of melamine phosphate to melamine cyanurate in the flame retardantcomposition is about 1:6 to about 2:1.
 5. A flame retardant adhesiveaccording to claim 1, wherein the flame retardant composition comprisesfrom about 30 wt % to about 60 wt % of the flame retardant adhesive. 6.A flame retardant adhesive according to claim 1, wherein the flameretardant composition comprises from about 35 wt % to about 50 wt % ofthe flame retardant adhesive.
 7. A flame retardant adhesive according toclaim 1, wherein the flame retardant composition comprises from about 38wt % to about 40 wt % of the flame retardant adhesive.
 8. A flameretardant adhesive according to claim 1, wherein the adhesive is apressure-sensitive adhesive.
 9. A flame retardant adhesive according toclaim 1, wherein the tape has a CTI rating of I.
 10. A flame retardantadhesive according to claim 1, wherein the tape is classified as flameretardant after being tested according to Section 6 of UnderwritersLaboratories UL 510, Seventh or Eighth Edition.
 11. A tape comprising asupport layer having two opposed, major surfaces, and the adhesive ofclaim 1 disposed on at least one of the major surfaces of the supportlayer.
 12. A tape according to claim 11, wherein the tape has a CTIrating of I.
 13. A tape according to claim 11, wherein the tape isclassified as flame retardant after being tested according to Section 6of Underwriters Laboratories UL 510, Seventh or Eighth Edition.
 14. Atape comprising a support layer having two opposed, major surfaces, anadhesive disposed on at least one of the major surfaces of the supportlayer, and a flame retardant composition comprising a melamine phosphateand a melamine cyanurate, the flame retardant composition being disposedin the support layer, on the support layer, or a combination thereof.15. A tape according to claim 14, wherein the melamine phosphatecomprises a melamine polyphosphate.
 16. A tape according to claim 14,wherein the melamine phosphate comprises a melamine pyrophosphate.
 17. Atape according to claim 14, wherein the weight ration of melaminephosphate to melamine cyanurate in the flame retardant composition isabout 1:6 to about 2:1.
 18. A tape according to claim 15, wherein thetape has a CTI rating of I.
 19. A tape according to claim 15, whereinthe support layer comprises a polyester, a polyolefin, a polyamide, or apolyimide.
 20. A tape according to claim 15, wherein the tape isclassified as flame retardant after being tested according to Section 6of Underwriters Laboratories UL 510, Seventh or Eighth Edition.